QImageIOHandler 类定义用于 Qt 中所有图像格式的常见图像 I/O 接口。 更多...
| 头： | #include <QImageIOHandler> |
| CMake: |
find_package(Qt6 COMPONENTS Gui REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Gui) |
| qmake: | QT += gui |
注意： 此类的所有函数 可重入 .
| enum | ImageOption { Size, ClipRect, ScaledSize, ScaledClipRect, Description, …, ImageTransformation } |
| enum | Transformation { TransformationNone, TransformationMirror, TransformationFlip, TransformationRotate180, TransformationRotate90, …, TransformationRotate270 } |
| flags | Transformations |
| QImageIOHandler () | |
| virtual | ~QImageIOHandler () |
| virtual bool | canRead () const = 0 |
| virtual int | currentImageNumber () const |
| virtual QRect | currentImageRect () const |
| QIODevice * | device () const |
| QByteArray | format () const |
| virtual int | imageCount () const |
| virtual bool | jumpToImage (int imageNumber ) |
| virtual bool | jumpToNextImage () |
| virtual int | loopCount () const |
| virtual int | nextImageDelay () const |
| virtual QVariant | option (QImageIOHandler::ImageOption option ) const |
| virtual bool | read (QImage * image ) = 0 |
| void | setDevice (QIODevice * device ) |
| void | setFormat (const QByteArray & format ) |
| void | setFormat (const QByteArray & format ) const |
| virtual void | setOption (QImageIOHandler::ImageOption option , const QVariant & value ) |
| virtual bool | supportsOption (QImageIOHandler::ImageOption option ) const |
| virtual bool | write (const QImage & image ) |
| bool | allocateImage (QSize size , QImage::Format format , QImage * image ) |
Qt uses QImageIOHandler for reading and writing images through QImageReader and QImageWriter 。还可以派生自此类，以使用 Qt 插件机制编写自己的图像格式处理程序。
调用
setDevice
() to assign a device to the handler, and
setFormat
() to assign a format to it. One QImageIOHandler may support more than one image format.
canRead
() 返回
true
if an image can be read from the device, and
read
() 和
write
() return true if reading or writing an image was completed successfully.
QImageIOHandler also has support for animations formats, through the functions loopCount (), imageCount (), nextImageDelay () 和 currentImageNumber ().
In order to determine what options an image handler supports, Qt will call supportsOption () 和 setOption (). Make sure to reimplement these functions if you can provide support for any of the options in the ImageOption 枚举。
要编写自己的图像处理程序，至少必须重实现 canRead () 和 read ()。然后创建 QImageIOPlugin that can create the handler. Finally, install your plugin, and QImageReader and QImageWriter will then automatically load the plugin, and start using it.
另请参阅 QImageIOPlugin , QImageReader ，和 QImageWriter .
This enum describes the different options supported by QImageIOHandler . Some options are used to query an image for properties, and others are used to toggle the way in which an image should be written.
| 常量 | 值 | 描述 |
|---|---|---|
QImageIOHandler::Size
|
0
|
The original size of an image. A handler that supports this option is expected to read the size of the image from the image metadata, and return this size from option () as a QSize . |
QImageIOHandler::ClipRect
|
1
|
The clip rect, or ROI (Region Of Interest). A handler that supports this option is expected to only read the provided QRect area from the original image in read (), before any other transformation is applied. |
QImageIOHandler::ScaledSize
|
4
|
The scaled size of the image. A handler that supports this option is expected to scale the image to the provided size (a QSize ), after applying any clip rect transformation (ClipRect). If the handler does not support this option, QImageReader will perform the scaling after the image has been read. |
QImageIOHandler::ScaledClipRect
|
3
|
The scaled clip rect (or ROI, Region Of Interest) of the image. A handler that supports this option is expected to apply the provided clip rect (a QRect ), after applying any scaling (ScaleSize) or regular clipping (ClipRect). If the handler does not support this option, QImageReader will apply the scaled clip rect after the image has been read. |
QImageIOHandler::Description
|
2
|
The image description. Some image formats, such as GIF and PNG, allow embedding of text or comments into the image data (e.g., for storing copyright information). It's common that the text is stored in key-value pairs, but some formats store all text in one continuous block. QImageIOHandler returns the text as one QString , where keys and values are separated by a ':', and keys-value pairs are separated by two newlines (\n\n). For example, "Title: Sunset\n\nAuthor: Jim Smith\nSarah Jones\n\n". Formats that store text in a single block can use "Description" as the key. |
QImageIOHandler::CompressionRatio
|
5
|
The compression ratio of the image data. A handler that supports this option is expected to set its compression rate depending on the value of this option (an int) when writing. |
QImageIOHandler::Gamma
|
6
|
The gamma level of the image. A handler that supports this option is expected to set the image gamma level depending on the value of this option (a float) when writing. |
QImageIOHandler::Quality
|
7
|
The quality level of the image. A handler that supports this option is expected to set the image quality level depending on the value of this option (an int) when writing. |
QImageIOHandler::Name
|
8
|
The name of the image. A handler that supports this option is expected to read the name from the image metadata and return this as a QString , or when writing an image it is expected to store the name in the image metadata. |
QImageIOHandler::SubType
|
9
|
The subtype of the image. A handler that supports this option can use the subtype value to help when reading and writing images. For example, a PPM handler may have a subtype value of "ppm" or "ppmraw". |
QImageIOHandler::IncrementalReading
|
10
|
A handler that supports this option is expected to read the image in several passes, as if it was an animation. QImageReader will treat the image as an animation. |
QImageIOHandler::Endianness
|
11
|
The endianness of the image. Certain image formats can be stored as BigEndian or LittleEndian. A handler that supports Endianness uses the value of this option to determine how the image should be stored. |
QImageIOHandler::Animation
|
12
|
Image formats that support animation return true for this value in supportsOption (); otherwise, false is returned. |
QImageIOHandler::BackgroundColor
|
13
|
Certain image formats allow the background color to be specified. A handler that supports BackgroundColor initializes the background color to this option (a QColor ) when reading an image. |
QImageIOHandler::ImageFormat
|
14
|
The image's data format returned by the handler. This can be any of the formats listed in QImage::Format . |
QImageIOHandler::SupportedSubTypes
|
15
|
Image formats that support different saving variants should return a list of supported variant names ( QList < QByteArray >) in this option. |
QImageIOHandler::OptimizedWrite
|
16
|
. A handler which supports this option is expected to turn on optimization flags when writing. |
QImageIOHandler::ProgressiveScanWrite
|
17
|
. A handler which supports this option is expected to write the image as a progressive scan image. |
QImageIOHandler::ImageTransformation
|
18
|
. A handler which supports this option can read the transformation metadata of an image. A handler that supports this option should not apply the transformation itself. |
[since 5.5]
enum QImageIOHandler::
Transformation
This enum describes the different transformations or orientations supported by some image formats, usually through EXIF.
| 常量 | 值 | 描述 |
|---|---|---|
QImageIOHandler::TransformationNone
|
0
|
No transformation should be applied. |
QImageIOHandler::TransformationMirror
|
1
|
Mirror the image horizontally. |
QImageIOHandler::TransformationFlip
|
2
|
Mirror the image vertically. |
QImageIOHandler::TransformationRotate180
|
TransformationMirror | TransformationFlip
|
Rotate the image 180 degrees. This is the same as mirroring it both horizontally and vertically. |
QImageIOHandler::TransformationRotate90
|
4
|
将图像旋转 90 度。 |
QImageIOHandler::TransformationMirrorAndRotate90
|
TransformationMirror | TransformationRotate90
|
Mirror the image horizontally and then rotate it 90 degrees. |
QImageIOHandler::TransformationFlipAndRotate90
|
TransformationFlip | TransformationRotate90
|
Mirror the image vertically and then rotate it 90 degrees. |
QImageIOHandler::TransformationRotate270
|
TransformationRotate180 | TransformationRotate90
|
Rotate the image 270 degrees. This is the same as mirroring it both horizontally, vertically and then rotating it 90 degrees. |
该枚举在 Qt 5.5 引入或被修改。
Transformations 类型是 typedef 对于 QFlags <Transformation>. It stores an OR combination of Transformation values.
另请参阅 QImageReader::transformation (), QImageReader::setAutoTransform ()，和 QImageWriter::setTransformation ().
构造 QImageIOHandler 对象。
[虚拟]
QImageIOHandler::
~QImageIOHandler
()
销毁 QImageIOHandler 对象。
[static, since 6.0]
bool
QImageIOHandler::
allocateImage
(
QSize
size
,
QImage::Format
format
,
QImage
*
image
)
This is a convenience method for the reading function in subclasses. Image format handlers must reject loading an image if the required allocation would exceeed the current allocation limit. This function checks the parameters and limit, and does the allocation if it is valid and required. Upon successful return, image will be a valid, detached QImage 为给定 size and format .
该函数在 Qt 6.0 引入。
另请参阅 QImageReader::allocationLimit ().
[pure virtual]
bool
QImageIOHandler::
canRead
() const
返回
true
if an image can be read from the device (i.e., the image format is supported, the device can be read from and the initial header information suggests that the image can be read); otherwise returns
false
.
When reimplementing canRead(), make sure that the I/O device ( device ()) is left in its original state (e.g., by using peek() rather than read ()).
另请参阅 read () 和 QIODevice::peek ().
[虚拟]
int
QImageIOHandler::
currentImageNumber
() const
For image formats that support animation, this function returns the sequence number of the current image in the animation. If this function is called before any image is read (), -1 is returned. The number of the first image in the sequence is 0.
If the image format does not support animation, 0 is returned.
另请参阅 read ().
[虚拟]
QRect
QImageIOHandler::
currentImageRect
() const
Returns the rect of the current image. If no rect is defined for the image, and empty QRect() is returned.
This function is useful for animations, where only parts of the frame may be updated at a time.
Returns the device currently assigned to the
QImageIOHandler
. If not device has been assigned,
nullptr
被返回。
另请参阅 setDevice ().
Returns the format that is currently assigned to QImageIOHandler . If no format has been assigned, an empty string is returned.
另请参阅 setFormat ().
[虚拟]
int
QImageIOHandler::
imageCount
() const
For image formats that support animation, this function returns the number of images in the animation. If the image format does not support animation, or if it is unable to determine the number of images, 0 is returned.
默认实现返回 1 若
canRead
() 返回
true
；否则返回 0。
[虚拟]
bool
QImageIOHandler::
jumpToImage
(
int
imageNumber
)
For image formats that support animation, this function jumps to the image whose sequence number is imageNumber . The next call to read () will attempt to read this image.
默认实现什么都不做，并返回
false
.
[虚拟]
bool
QImageIOHandler::
jumpToNextImage
()
For image formats that support animation, this function jumps to the next image.
默认实现什么都不做，并返回
false
.
[虚拟]
int
QImageIOHandler::
loopCount
() const
For image formats that support animation, this function returns the number of times the animation should loop. If the image format does not support animation, 0 is returned.
[虚拟]
int
QImageIOHandler::
nextImageDelay
() const
For image formats that support animation, this function returns the number of milliseconds to wait until reading the next image. If the image format does not support animation, 0 is returned.
[虚拟]
QVariant
QImageIOHandler::
option
(
QImageIOHandler::ImageOption
option
) const
Returns the value assigned to option 作为 QVariant . The type of the value depends on the option. For example, option(Size) returns a QSize variant.
另请参阅 setOption () 和 supportsOption ().
[pure virtual]
bool
QImageIOHandler::
read
(
QImage
*
image
)
Read an image from the device, and stores it in
image
。返回
true
if the image is successfully read; otherwise returns false.
For image formats that support incremental loading, and for animation formats, the image handler can assume that image points to the previous frame.
另请参阅 canRead ().
Sets the device of the QImageIOHandler to device . The image handler will use this device when reading and writing images.
The device can only be set once and must be set before calling canRead (), read (), write (), etc. If you need to read multiple files, construct multiple instances of the appropriate QImageIOHandler 子类。
另请参阅 device ().
Sets the format of the QImageIOHandler to format . The format is most useful for handlers that support multiple image formats.
另请参阅 format ().
Sets the format of the QImageIOHandler to format . The format is most useful for handlers that support multiple image formats.
This function is declared const so that it can be called from canRead ().
另请参阅 format ().
[虚拟]
void
QImageIOHandler::
setOption
(
QImageIOHandler::ImageOption
option
, const
QVariant
&
value
)
设置选项 option 采用值 value .
另请参阅 option () 和 ImageOption .
[虚拟]
bool
QImageIOHandler::
supportsOption
(
QImageIOHandler::ImageOption
option
) const
返回
true
若
QImageIOHandler
支持选项
option
；否则返回
false
。例如，若
QImageIOHandler
支持
Size
选项，supportsOption(Size) 必须返回 true。
另请参阅 setOption () 和 option ().
[虚拟]
bool
QImageIOHandler::
write
(const
QImage
&
image
)
写入图像
image
到赋值设备。返回
true
当成功时；否则返回
false
.
默认实现什么都不做，且仅返回
false
.